Posts
109
Joined
10/29/2021
Location
Brevard, NC
US
Edited Date/Time
11/9/2021 10:10am
Sup bike nerds!
Wanted to start this thread to pick some brains about high pivots. A team mate of mine has a Kona Process X and complained to me about pedal kickback when riding chunky terrain. Since it is a linkage activated single pivot, the suspension kinematics are impacted by pedal force. The hub he is using doesn't have that high of engagement so Im not worried about that affecting things. Being the mechanic that wants to make bikes faster, I started down the wormhole of trying to reduce the kickback he was feeling.
My thinking is that raising the chain to be at or above the pivot point will reduce the amount of resistance he feels when the suspension compresses.
To achieve this, I am wanting to design a DIY idler that mounts to the ISCG-05 chain guide mounts.
EDIT*
Pedal Kickback might not be the correct term for the sensation the rider is feeling. In his explanation, he described a fighting feeling coming from the cranks while descending a pretty chunky trail here in Pisgah.
Going back to basic geometry, taking the 'Triangle' shape of the drivetrain and adding another solid point would essentially create a parallelogram where the lengths of the sides would stay the same.
While not being as drastic of a change, we've got some downtime this offseason and want something to keep us occupied.
Wanted to start this thread to pick some brains about high pivots. A team mate of mine has a Kona Process X and complained to me about pedal kickback when riding chunky terrain. Since it is a linkage activated single pivot, the suspension kinematics are impacted by pedal force. The hub he is using doesn't have that high of engagement so Im not worried about that affecting things. Being the mechanic that wants to make bikes faster, I started down the wormhole of trying to reduce the kickback he was feeling.
My thinking is that raising the chain to be at or above the pivot point will reduce the amount of resistance he feels when the suspension compresses.
To achieve this, I am wanting to design a DIY idler that mounts to the ISCG-05 chain guide mounts.
EDIT*
Pedal Kickback might not be the correct term for the sensation the rider is feeling. In his explanation, he described a fighting feeling coming from the cranks while descending a pretty chunky trail here in Pisgah.
Going back to basic geometry, taking the 'Triangle' shape of the drivetrain and adding another solid point would essentially create a parallelogram where the lengths of the sides would stay the same.
While not being as drastic of a change, we've got some downtime this offseason and want something to keep us occupied.
Kickback should be below average even though it is a single pivot. You can calculate critical speed above which you would not encounter any kickback at all (angular velocity of the rear wheel equals angular velocity of the hub).
I suspect the Kona to be in the 10kp/h range, so i wouldn´t bother compromising pedaling performance.
An add on idler would also be cool for some bikes like the Marin wolf ridge which had an insane amount of pedal feedback.
Like Big Bird mentioned, if you are going to make it, make it _THICC_. Billet aluminium, as thick as it can be between the tab and the chainring, fill any space between the chainring and the frame/swingarm, etc. The bike is carbon and doesn't have many useable bolts close by (shock mounts and/or pivots), so it will be hard to use any of those.
The main differentiator in the above point is the main pivot. Honestly it appears to be fairly low for both single pivot and quite a few FSR applications, so I'm kind of surprised pedal kickback is the main issue here (I'd say it should be somewhat low compared to some other bikes, same goes for antisquat values). And adding an idler will thus make it squat HARD (even more so than I originally anticipated).
But still, if it needs to be done, how is the main pivot constructed? Is there a spacer between the swingarm and the bearing? Where is the bearing? Is it possible to sandwich an additional blade like part between the swingarm and the blade to provide additional support? Sadly Kona doesn't provide any technical drawings/manual (cycling industry SERIOUSLY needs to rethink some of the practices... Geez!) so I can only imagine how the swingarm is mounted. If you have any closeup (disassembled would be better!) pics of the pivot, that would also help.
But, honestly, I would advise against doing something like this, unless you have the machines, time and knowledge to whip it up quickly and cheaply just to test it out. Unless something weird happens with physics, the bike should pedal horribly with an added idler.
While I agree that it is not the most ideal solution to any problem, seeing the rise of the high pivot in DH racing has sparked my, and my team mate's interest in testing something out.
We aren't concerned with pedaling dynamics such as the anti-squat. Regardless of suspension design or gear selection, we just thought it would be a cool idea to come up with something that could possibly affect the way the bike rides.
I understand the "high pivot" is a buzz word right now (doing it for the clicks), but the bummer is that title doesn't even address the main concern of the writer, "how can I reduce pedal kick back? Is an idler the answer?"
All this does is create more confusion in the industry and it doesn't help the consumer.
Quick test is to do a chainless and normal run.
How is the chain length and clutch condition? If the chain is too long or it runs down the block in smaller cogs with the pulley right back then the lower section of chain will be pulling on the cranks too.
If you do go ahead with the idler make it all burley as hell, and the larger diameter/higher tooth count the better. Also take care where you place it to get the desired change. A more shallow turn around the pulley will put less load on it, so in general I would think the further back you can put it the better too as it will make everything much easier
No matter how good your suspension is, you are going to feel feedback through your feet. Until we create hover crafts, that is just how it works.
EDIT: So you can read it.
A bike is far more than its obvious features and i agree our head is messing with our judgement a lot. So keep tinkering anyhow, whatever everybody is suggesting online. Nothing beats experience you made yourself, on your terrain, with your abilitiy and your riding style. There is no such thing like a perfect bike for everybody.
I noticed a change for the better swapping a 30T to a 32T on a Commencal Meta AM. Would have been interesting to repeat runs and change from the 30T to a 34T or 36T if it would fit.
If I had to wager, I'd say the feeling in his feet is definitely caused by... something. His fork could be too soft and he's shifting weight onto his feet, it could be because his compression is too firm or too soft, his rear shock could be too stiff or too soft, it could be because his feet are tired, or his tires could be too low in pressure. It could be a lot of things. If it were me, I'd start with suspension setup and body position, and I'd recommend video taping your friend through that same section of trail to diagnose if something looks visibly out of whack. Video can be incredibly helpful for these things.
Also worth reiterating that idler pulleys are subjected to ENORMOUS amounts of torque from pedaling. Big Bird alluded to this when he mentioned finding an additional mounting point for the idler backplate, and Primoz alluded to this when he recommended making that plate THICC. All of your pedaling torque is transferred through an idler pulley, essentially pulling it down as you pedal. Chainguide pulleys and thin aluminum chainguide plates simply don't see this kind of torque because the chain is slack on the bottom side of the chainring and not under load when you're pedaling. The only time chainguide plates and ISCG tabs see that level of torque is when you hit a rock with the bashguard, and that often results in catastrophic failure for the part. It's not the sort of force you'd want to inflict on a part every time you pedal. So if you're going to give it a try, I agree with Primoz and Big Bird that you'll want to drastically overbuild it beyond what seems necessary if it's going to be functional.
I shared my extended thoughts on pedal kickback in this Vital article here, concluding that pedal kickback is definitely not a thing you need to worry about: https://www.vitalmtb.com/features/MTB-ADVICE-with-Team-Robot-ANSWERS-2,…
Google "Kona Brake Therapy" to see what it looks like - compared to making an idler out of thin air on a carbon frame a floating brake would be relatively simple, except for the frame attachment point.
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